1. Field of the Invention
This invention relates to a process for preparing polyacetylenes and more particularly to preparing polyacetylenes by catalytic polymerization. The invention also relates to substituted polyacetylenes prepared by this process.
2. Description of the Prior Art
Polyacetylenes are a kind of polymer, i.e., they belong to the group of macromolecular, natural or synthetic compounds which are formed, e.g., by polymerization from monomers. In polymerization, macromolecules are constructed by chemical reactions. At each reaction step a monomer molecule M is added to a polymer molecule P: P*.sub.m +M.fwdarw.P*.sub.n+1. In this expression, P* signifies the presence of an activated state. This active center is located at either end of the growing polymer chain. Suitable monomers for polymerization include unsaturated monomers such as acetylene, ethylene, styrene and acrylonitrile which combine to form long molecular chains having different degrees of polymerization. Polyacetylenes can be prepared simple by introduction of the acetylene into a solution containing a catalyst. By suitable choice of catalyst a sheet can also be formed (H. Shirakawa, S. Ikeda, Polymer J. 2,231, 1971). The preparation of polyacetylene in powder form is also known (L. B. Luttinger, J. Org. Chem. 27, 1591, 1962).
Polyacetylenes are made up, as pointed out above, of polymer chains. In such chains the bonds between the carbon atoms are alternately double and single bonds, as shown in the following example: ##STR1## The polyacetylenes prepared by known processes become brittle very soon after they are prepared, and they react with oxygen, especially when they are exposed to the action of air and/or UV-light. From the structure shown above, the elementary analysis of polyacetylene must yield a C/H-ratio of 1, since long chains are present in the polymer, and thus the hydrogen content of the terminal positions of the chain can be neglected. In practice, however, the measured C/H-ratio is not equal to 1. This is caused by crosslinking of the chains which make up the polymer. This crosslinking occurs both in the presence and absence of oxygen and/or UV-light. The consequence of this reactivity between the chains of the polymers is a relatively high degree of crosslinking and a relatively high molecular weight, over 5.10.sup.5. The crosslinking reaction taking place in polyacetylenes can be detected because the polyacetylene experiences an increase in weight of 15% over a two-weeks period. Simultaneously, carbonyl bands can be detected in the infrared spectrum. Furthermore, the polyacetylene exhibits a decrease in its elasticity. Cracks can also be detected in the polyethylene. This crosslinked chain has the disadvantage that the polymer itself no longer softens at temperatures above 300.degree. C. It is also no longer possible to dissolve the polymer in a solvent.
In order that polyacetylenes can be used in injection molding or coating, however, these are necessary conditions which must be unconditionally fulfilled.
Therefore, a need has continued to exist for a polyacetylene which remains soluble and meltable because it is not subject to cross-linking, particularly by the action of oxygen.